1. Field of the Invention
This invention relates to a constant speed drive mechanism and more particularly to a low-speed disconnect between an input and output that cannot accidentally return to a reengaged position.
2. Description of the Prior Art
In many areas, and particularly in the aircraft field, it is required to operate certain accessories with a constant frequency source of power. Accordingly, a generator or alternator must be driven at a constant speed. The source of the driving power is quite variable due to the demands for the higher or lower speeds from the prime mover.
Between the prime mover and the constant speed drive transmission is a form of clutching arrangement which is adapted to connect the output of the prime mover to the input of the transmission in such a way that the driving train can be interrupted under certain conditions, for instance, upon overheating in the transmission, generator breakdown in the system, or the like, where the prime mover is still operating. This can best be handled by disconnecting the prime mover from the constant speed transmission so as to prevent damage to the transmission and/or to the generator.
Heretofore, a plunger-actuated gear element was moved into engagement with a worm which in turn was splined to a coupling member whereby the worm moved along the gear element to disengage the coupling member from the input shaft. Under normal high speed conditions, the plunger-actuated gear element will drop in behind the worm to hold the coupling member in disengaged relationship with respect to the input member. However, when the speed of the input member is relatively low, the plunger-actuated gear element and worm are effective to disconnect the coupling member from the input shaft, but, even though the teeth of the coupling member are disengaged from the teeth on the input shaft, the space therebetween is relatively little, and there is not sufficient speed or momentum in the coupling member to drive the worm off the end of the plunger-actuated gear element. As a result, vibration caused by the prime mover can cause the worm to gradually rotate back relative to the plunger-engaged gear until the teeth on the coupling member come in contact with the teeth on the input shaft, causing damage to the teeth and, in some cases, reengaging the coupling member to drive the transmission and the generator even though one or the other or both may have failed.